1. Technical Field
The present invention relates to a thin film transistor and a method for manufacturing the same, and more particularly, to an organic thin film transistor and a method for manufacturing the same.
2. Discussion of the Related Art
Generally, a thin film transistor is used as a switching element for a display device. The thin film transistor may be formed of various materials, for example, silicon and organic materials. The organic thin film transistor is formed of an organic semiconductor material. Also, the organic thin film transistor uses a flexible substrate instead of a glass substrate. Except that the organic thin film transistor uses the organic semiconductor material and the flexible substrate, the organic thin film transistor is similar in structure to the silicon thin film transistor.
FIG. 1 is a cross section view illustrating a related art organic thin film transistor. As shown in FIG. 1 the related art organic thin film transistor includes a gate electrode 52a of a metal material formed on a lower substrate 51; a gate insulation layer 53 formed on the lower substrate including the gate electrode 52a; source and drain electrodes 55a and 55b overlapped with both edges of the gate electrode 52a and formed on the gate insulation layer 53; and an organic semiconductor layer 54 formed on the gate insulation layer 53 including the source and drain electrodes 55a and 55b. In this case, the source and drain electrodes 55a and 55b may comprise an inorganic metal material of palladium (Pd) or silver (Ag).
For the above-mentioned organic thin film transistor, the gate insulation layer 53 may comprise an organic material. The gate insulation layer 53 of the organic material is treated with plasma to improve an adhesive strength between the gate insulation layer 53 of the organic material and the source/drain electrodes 55a/55b of the metal material.
However, the gate insulation layer treated with plasma has hydrophilic properties. If the organic semiconductor layer is formed on the gate insulation layer with hydrophilic properties, the organic semiconductor layer grows with small grains.
FIG. 2A shows the grain structure of the organic semiconductor layer formed on the gate insulation layer having hydrophobic properties which is not treated with plasma. FIG. 2B shows the grain structure of the organic semiconductor layer formed on the gate insulation layer having hydrophilic properties which is treated with plasma. As comparing FIG. 2A with FIG. 2B, the grain size of the organic semiconductor layer formed on the gate insulation layer having hydrophilic properties is smaller than the grain size of the organic semiconductor layer formed on the gate insulation layer having hydrophobic properties.
If the organic semiconductor layer having small grain size is formed on the gate insulation layer having hydrophilic properties, a grain boundary increases in number due to the small grain size. Since the grain boundary functions as a charge trap site, the electric properties of the organic semiconductor layer deteriorate.